This invention relates to a new and improved resin-impregnated fabric, which upon curing, is suitable for use as a wet friction material in transmission couplings, automatic lockers, limited slip differentials, smart clutches, brakes, synchronizers and the like. More particularly this invention concerns the use of woven or braided fabric utilizing continuous untwisted carbon filament yarn or other fiber, and impregnating this material with a modified cyanate ester oligomer at low concentration levels for such use after curing.
The use of woven fabrics containing different resins such as phenolics, pyrolytic carbon, epoxy, etc., are well known in the industry and have been used for many years in the aerospace and automotive industries.
Also, the use of resin-impregnated fabric cured composites as wet friction materials in transmission and brake components is well known, and typical publications concerning this use are disclosed in U.S. Pat. Nos. 4,700,823; 5,662,993; 5,842,551; 5,895,716; 5,952,249; 6,060,536; 6,132,877 and, 6,135,256. In wet friction applications, the flow of hydraulic fluid and the hydrodynamic film formed between the driven and non-driven member of the transmission play an important role in providing effective performance as transmission couplings.
The materials described in these patents may have various problems associated with their use. For example, in the case of U.S. Pat. No. 5,662,993 to Winckler there is a problem with the type of fabric employed, which is woven with bundles of twisted, stretch-broken filaments. The problem arises since the loose strand ends described in those patents can become worn due to abrasion. Eventually these loose ends may tend to break off, causing contamination due to the formation of debris within the fabric which then becomes plugged; this debris tends to interfere with oil circulation.
Moreover, since the fabric material used in the Winckler patents is bulky, this bulkiness requires a fairly large amount of phenolic (or other) resin to be employed for effectiveness.
Also in the Winckler patent, the twisted bundles of discontinuous staple fibers in the fabric are made by stretch breaking, twisting and spinning, which is similar to cotton yarn production. However, this process of carbon staple yarn production is expensive. In addition, since the lengths of these discontinuous filaments can be in the range of about ¼″-4″, the fabric formed from this fuzzy type of yarn does not produce the same strength as fabric formed from continuous, untwisted filament strands.
Phenolic resins have been in use for many years because their high cross linking density and high aromatic ring content results in a high glass transition temperature and a high char yield. However, because of their high cross linking density, phenolic resins tend to be more brittle and resemble crystalline materials which have poor adhesion to carbon fibers. Also, during the phenolic curing stage, some reaction by products are emitted which cause porosity and bulkiness.